This instrumentation application is to purchase a Scanning Transmission Electron Microscope (STEM) with X-ray analytical capabilities; the College of Arts and Sciences has committed $150,000 in matching funds for this instrument. This proposed STEM (the Philips 400T with an EDAX analyzer) will be capable of transmission electron microscopy (TEM), STEM, and scanning electron microscopy (SEM) using either secondary (SE) or backscattered electron (BSE) emissions and quantitative elemental analysis will be possible in all modes of operation. TEM with thin sections and STEM with thick sections will be used by the research groups lead by Schatten, Freeman and Lipner to study, with high resolution, the three-dimensional organization of the cytoskeleton in eggs during fertilization and neuroendocrine secretory cells. Darkfield TEM and STEM of DNA, RNA, nucelosomes and immunoglobulins will be investigated by the laboratories of Taylor, Marzluff, Rill and Roux, respectively; these studies will use both stained or shadowed and unstained specimens from which more accurate measurements of molecular dimensions will be possible. SEM using either or both SE or BSE signals will be used by Schatten's and Roux's teams to elucidate the events at the cell surface during sperm incorporation and metabolic activation at fertilization and during lymphocyte activation and antibody binding, respectively. Stereo pairs using the goniometer stage will be used with thick sections observed by STEM to reconstruct the internal and intracellular arrangements in their respective systems of investigations. Energy dispersive X-ray analysis will be performed in all three modes to localize intracellular (Ca++) by Schatten and to detect molecular tags containing iodine, gold or iron labeling antibodies, lectins, hormones or their receptors by the laboratories of Freeman, Lipner, Roux and Schatten. The chosen instrument will replace a Philips 200 purchased 16 years ago for which the manufacturer no longer makes replacement parts. The reliability, capabilities, and service of this STEM makes it the instrument of choice. Its acquisition will permit an upgrading of the NIH-supported research on the cellular and molecular basis of reproduction, development, differentiation and aging.